JPS62206514A - Switching type variable power optical system - Google Patents

Abstract

PURPOSE:To easily attain a high variable power ratio by inserting selectively two auxiliary lens systems having positive and negative refracting powers respectively onto the optical axis behind a main lens system and selecting and using one of these auxiliary lens systems. CONSTITUTION:The first and second auxiliary lens systems 2 and 3 are so arranged that either of them can be inserted onto and removed from the optical axis behind a main lens system 1. In a figure A, the main lens system 1 and the first auxiliary lens system 2 constitute the first photographing system which has a short focal length and a wide field angle, and two lens systems having positive refracting powers are joined to increase the refracting power of the whole of the system. In a figure B, the first auxiliary lens system 2 shown in the figure A is removed from the optical axis of the main lens system 1 and the main lens system 1 is fed out to the object side, and only the main lens system 1 constitutes the second photographing system in the standard state which has a middle focal length. In a figure C, the main lens system 1 shown in the figure B is fed out to the object side furthermore and the second auxiliary lens system 3 is set onto the optical axis behind the main lens system 1 to constitute the third photographing system having a long focal length.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a switching type variable magnification optical system suitable for photographic cameras, video cameras, etc. Figure 9 shows the common use of the main lens system in P, with two auxiliary lens systems removably placed on the image plane side of the main lens system to change the focal length of the entire system. The present invention relates to a small-sized switching type variable magnification optical system that can easily provide high-performance optical performance with a high variable magnification.

(Prior art) Conventionally, the focal length t of the entire system is determined by attaching it to the object side or image field side of the main lens system and keeping the focal plane of the entire system at a constant position.
An auxiliary lens system that changes the tat, a so-called converter lens, has been proposed a number of times. Among these, the so-called front converter method, in which a converter lens is attached to the object side of the main lens system, was unsuccessful because it was difficult to miniaturize the entire system since the converter lens system is important.

On the other hand, a so-called rear converter method, in which a converter lens is installed in the image field of a lens system, is advantageous in reducing the size of the lens system compared to the front converter method, but it requires correction of aberrations and increases the total number of lenses. The overall length of the lens has to be increased.

JP-A No. 59-29214 proposes a wide converter lens that employs a rear converter method in which all lens systems with positive refractive power are installed behind the main lens system to shorten the focal length of the entire system. ing.

However, the wide converter lens proposed in the same publication has a small variable power ratio of 2 or less when attached to a converter reflex X', and when a converter lens is attached, the overall length of the lens becomes longer and tends to become larger.

In addition, in Japanese Patent Publication No. 58-38778, two lens systems i, a standard lens and a telephoto lens, are arranged side by side facing the subject.
We have proposed a compact variable magnification optical system that uses a movable reflector built into the camera body to selectively use one of the lens systems 1r. However, the variable magnification optical system has a drawback in that since the focal lengths of the two lens systems are different, the amount of extension of the lens systems relative to the object distance is different.

For example, when this is applied to an autofocus camera, the extension f of each lens system must be changed between the standard state and the telephoto state, which tends to complicate the internal mechanism of the camera.

(Problems to be Solved by the Invention) The present invention solves the problem that no matter which one of the three photographing systems is used, i' Providing a switching type variable magnification optical system that maintains constant t and easily obtains a high variable magnification ratio of about 3? purpose.

(Rounding means to solve the problem) A main lens system with a positive refractive power, an fMl auxiliary lens system with a positive refractive power, and a second auxiliary lens system with a negative refractive power behind the main lens system. A first photographing system consisting of the king lens system and the first auxiliary lens system, a second photographing system consisting only of the main lens system, and a second photographing system consisting only of the main lens system; One of the three photographing systems of the third photographing system using the second auxiliary lens system is configured to be selectable.

Other q# images of the present invention are described in the Examples.

(Embodiment) FIG. 1, @, and 0 are schematic diagrams of the optical systems of the 11th, 21st, and 3rd imaging systems of the switching type variable magnification optical system of the present invention, respectively. In the figure, 1 indicates a main lens system S2 having a positive refractive power, and 3 indicates a second auxiliary lens system 14 having a negative refractive power formed by a photosensitive surface. One of the 1S second auxiliary lens systems is arranged behind the main lens system so that it can be inserted and removed on the optical axis of the main lens system.

The figure shows a first photographing system consisting of a main lens system 1 and a first auxiliary lens system 2, which constitutes a first photographing system with a short focal length and a wide angle of view. That is, by combining two lens systems that both have positive refractive power, the overall refractive power is strengthened by νζ, and the focal length of the entire system is shortened.

In the same case (6), when the IKl auxiliary lens system 2 is retracted from the optical axis of the main lens system l from the state shown in (5) of the same figure, the Republic King lens system 1t is extended to the body side, and only the King lens system L is in the middle. This constitutes a second photographing system with a standard focal length.

The main lens system 1 is moved further toward the object side from the state shown in (6) in the same figure, and the second auxiliary lens system 3 is moved to the main lens system 1.
By looking at the RC on the rear optical axis of the lens, the focal length of the third
Photography system t-configured.

In other words, the lens structure as a whole is of a telephoto type and allows a long focal length to be easily obtained.

In this embodiment, the 1st-% 2nd and 3rd imaging systems are sequentially
In addition to the reversible switching method, direct switching from the first imaging system to the third imaging system or vice versa may be used.

Conventionally, a variable magnification optical system has been constructed by cutting two copying systems, which makes it difficult to obtain an optical system with a high variable magnification.

However, in this embodiment, three lens systems are used, and by appropriately combining all of these lens systems, it is a variable power optical system with a simple structure and a high zoom ratio capable of ranging from wide-angle photography to telephoto photography. easily achieved.

In this example, whether the main lens system is used in any of the US, 2nd, and 3rd imaging systems? It is arranged on the subject side, and when focusing, a part or all of the main lens system is moved.In both shooting systems, the lens movement t for the same subject is made equal, and for example, an automatic focus detection system is used.
This is used to simplify the mechanism for the next time.

Although the object of the present invention is achieved with the above configuration, in order to further reduce fluctuations in various aberrations before and after switching and maintain good optical performance of the entire screen, it is important to satisfy all of the following conditions.

That is, the focal lengths 111 of the 11th, second, and third imaging systems are all fw
, fM, and fT, and the principal point distance between the main lens system and the first auxiliary lens system in the first RFI shadow system is EWS, and the principal point distance tFJT between the main lens system and the second auxiliary lens system in the second shadow system is When 0.1 < ]iW/fy (< 0
-9 ・・・・・・・・・(21α1 kum/fy1 < 0.9 ・−・・・・・・
Each lens system is configured to satisfy all conditions (3).

Conditional expression (1) is intended to allocate the zooming dead money in a well-balanced manner when switching from the first imaging system to the three imaging systems in order, and to properly correct aberrations in each imaging system. If the upper limit is exceeded, the magnification ratio when switching from the 1st m shadow system to the 2nd imaging system becomes too thick, making it difficult to correct aberrations in the 1st imaging system.9 Conversely, the lower limit +1i! If the value exceeds t-, the zoom ratio when switching from the second imaging system to the third imaging system becomes too large, making it difficult to correct aberrations in the third imaging system.

Conditional expression (2) is for appropriately setting the principal point interval between the main lens system and the first auxiliary lens system in the first imaging system.
If the lower limit is exceeded, the main lens system and the first auxiliary lens system will be too close to each other, making it difficult to configure the entire lens system.If the upper limit is exceeded, the positive refractive power of the first auxiliary lens system will be excessive and the positive refractive power will be too large. The Petzval sum increases, and as a result, the curvature of field increases in the negative direction, and many lows occur over the entire screen, which is not good.

Conditional expression (3) is to appropriately set the principal point distance between the main lens system and the second auxiliary lens system in the third photographing system, and 1
If the lower limit is exceeded, the main lens system and the second auxiliary lens system will be too close to each other, making it difficult to configure the lens system.
If it exceeds i, the negative refractive power of the second auxiliary lens system becomes excessive, the negative Petzval sum increases, and as a result, the 1-parameter curvature increases in the positive direction, which is undesirable.

Next, an ali implementation sequence of the present invention is shown. In the numerical example, R1 is the radius of curvature of the lens surface of the first scan from the object side,
Di is the first lens thickness from the object side and the air gap N
Nl and vi are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

D7S in Numerical Example IK D6Fi in Numerical Example 2 This is the interval when the auxiliary lens thread tube is attached to each main lens system. Further, R, D, N, and ν of the auxiliary lens system are expressed by the numbers when attached to the main lens system.

Number li! Example 1 Main lens system F-70FNO-1:5,6 2ω-341R1=
21.59 D l-101N l-1,7
7250y 1-49.6a '2- zrss,s
s o z-t3<R3--51L66 D
3■2hoo N 2-1.66680 ν
2-31OR4-212404-L81 R5= -7432D 5-L44 N 3-
L58144 v 3=40.7R6”7125
．． 00 D 6=! 48 N 4-1.8
1600 v 4-4a6R7--30,58 First auxiliary lens system D 7-L49 R8-21,09D 8-227 N 5-L8
8300 ν 5-4α8R9 fog 365.65
D 9-1.12RIO--2179010■LO
ON 6-L59270 ν 6-35.3R1
1-2L55 Dll-1,15R12--317
3D12-188 N 7■1.69350
ν 7 snow 53.2R13 praise -1482 whole system; F-35, F'N0-1:R8, 2ω-6&4
“Second auxiliary lens system D 7 nose Z71 R8=-109,1308-197N 5-1.67
270 v 5-3LIR9--24,5809
-L66 RIG--2LO0010-1,00N 6-L88
300 ν 6-4α8R11■ 96.43
Dll■α10R12= 5412 D12-
R95N 7-L53256y 7-4! L
9R13 Gen-5 & 89 ・All series; F-105, F'N0-1:1lL5, 2ω
-23iEy/ 7M -0,21 ET//M-0,21 Numerical Example 2 Main lens system F-80FNO-1: Mr. 6 2ω-3ατR1=
20.95 D 1-4.33 N l”1.
77250 v l-4'L6R2-6a13
D 2-Z91R3--46&96 D
3-101 N 2-L69895 ν 2
-30.1R4-19, 33D 4-&62 R5-7/L87 D 5-&37 N
3-1.88300 y 3=40.8R6--
112.90 First auxiliary lens system D 6 thin 1.62 R7-30,0507-L47 N 4-1.88
300 ν 4-40.8R8-302,09D
8-L64 R9--4L11 D 9-1.67 N
5-L59270 ν 5-35.3RIO-2
7,27010-1,33 R11--44,33Dll-1,52N 6-1.
69350 ν 6-512R12--2165 whole system; F'-50, FNO-1:3.5, 2ω-4
a8° Second auxiliary lens system D 6-1.81 R7--50, 2607-IJ4 N 4-1.
6727Q v 4-3LIR8--11197
D 8-1.76 R9" -17,35D 9=LOON 5-1.88
300y 5-4 (L8110-11Z85
DlG-0,10R11-5LO7Dll-122N
6-L53256 ν 6-45.9R12--
3LO1 whole system; F-135, FNO-1:9L5, 2ω-1
&! EV/fyl -0,21 ~/fy1-0.21 (Effect of the invention) According to the present invention, two auxiliary lens systems with positive and negative refractive powers are selectively inserted on the rear axis of the king lens system. By layering the three imaging systems, one of these can be selected.
By selecting and using the lens system, a high variable power ratio can be easily obtained, and the lens system's shift*tv is made equal when focusing on the same object in any imaging system. A variable magnification optical system can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG.
FIG. 4 is a cross-sectional view of a lens of numerical embodiment 1.2 of the present invention, and FIG. 3 is a cross-sectional view of a lens of numerical embodiment 1.2 of the present invention. In Figures 1 to 5, (A) Fi 1st photographing system, S = 2nd photographing system, and (Q indicates the 3rd photographing system. In the figure, 1 is the king lens system, and 2 is the first auxiliary lens system. The second auxiliary lens system 13 is a photosensitive surface.

Claims (2)

[Claims] (1) A main lens system with positive refractive power, and a first auxiliary lens system with positive refractive power and a second auxiliary lens system with negative refractive power behind the main lens system, on the optical axis of the main lens system. A first photographing system comprising the main lens system and the first auxiliary lens system, a second photographing system comprising only the main lens system, and a second photographing system comprising the main lens system and the second auxiliary lens system, which are removably installed. Third
A switching type variable magnification optical system characterized in that one of three photographing systems can be selected. (2) The switching system according to claim 1, characterized in that in each of the first, second, and third photographing systems, focusing is performed by moving a part or all of the main lens system. Variable magnification optical system.